Method and means for variation of magnetic strength of permanent magnetic drums



July 18, 1961 H. w. BUUS 7 METHOD AND MEANS FOR VARIATION OF MAGNETICSTRENGTH OF PERMANENT MAGNETIC DRUMS Filed Jan. 14, 1959 3 Sheets-:Sheet1 Harold W Buys July 18, 1961 w, uus 2,992,737

METHOD AND MEANS FOR VARIATION OF MAGNETIC STRENGTH OF PERMANENTMAGNETIC DRUMS Filed Jan. 14, 1959 5 Sheets-Sheet 2 92 3 90 .IEVE 2211?"Harold W. Baas 7 @kgm w jw 5 111 15 y 1961 H. w. Buus 2,992,737

METHOD AND MEANS FOR VARIATION OF MAGNETIC STRENGTH OF PERMANENTMAGNETIC DRUMS Filed Jan. 14, 1959 3 Sheets-Sheet 3 ha 22cm Ham/0 W BuusUnited States Patent 2,992,737 METHOD AND MEANS FOR VARIATION OF MAG-NETIC STRENGTH F PERMANENT MAGNETIC DRUMS Harold W. Buus, Hales Corner,Wis, assignor to Indiana General Corporation, a corporation of IndianaFiled Jan. 14, 1959, Ser. No. 786,873 10 Claims. (Cl. 209-223) Thisinvention relates to a method and means for adjusting the magnetic fieldof magnetic separators and particularly relates to means for adjustingthe useful magnetic field strength of a permanent magnet separator byadjusting the reluctance of a leakage path for magnetic flux emanatingfrom the permanent magnet assembly of the separator.

The invention is particularly applicable to varying the magnetic fieldstrength of permanent magnetic drums as used for either wet or dry typemagnetic separations. Control of the magnetic field strength, in manyseparations, enables selective separation of materials of varyingmagnetic responsiveness and the production of either magnetic ornon-magnetic products of greater purities.

In a preferred embodiment of the invention, a shorting bar or armatureis provided defining an auxiliary path for magnetic lines of flux fromthe permanent magnet assembly. The presence of the auxiliary path ofmagnetic material reduces the total magnetic lines of force available inthe separating zone. By controlling the amount and/ or position of themagnetic material defining the auxiliary path, the useful magnetic fieldstrength of the separator is varied.

It is therefore an important object of the present invention to providea simple and flexible mechanical means for varying the magnetic fieldstrength in a magnetic separator.

A further object of the invention is to provide a permanent magnetseparator of readily adjustable magnetic field strength.

Another object of the invention is to provide a permanent magneticseparator whose magnetic field over a predetermined separating zone isreadily adjusted to pro vide optimum separation under varyingconditions.

Other objects, features and advantages of the present invention will beapparent from the following detailed description taken in connectionwith the accompanying drawings, in which:

FIGURE 1 is a cross sectional view of a drum type permanent magnetseparator for use in wet type separations and embodying the teachingsand principles of the present invention;

FIGURE 2 is a longitudinal sectional view of the Wet type separator ofFIGURE 1;

FIGURE 3 is a cross sectional view similar to FIG- URE 1 butillustrating a modified means for adjusting the useful magnetic fieldstrength of the separator;

FIGURE 4 is a fragmentary somewhat diagrammatic perspective view of awet type permanent magnet separator and illustrating a furthermodification of the present invention; and

FIGURE 5 is a cross sectional view similar to FIGURE 1 but illustratinga dry-type permanent magnetic drum separator in accordance with thepresent invention.

A permanent magnetic separator for wet type separations may have aslurry feed introduced to the separator by means of suitable piping forflow under a submerged lower portion of a separator drum such asindicated at 11 in FIGURE 1, the material to be separated flowinggenerally in the direction indicated by the arrow 12 in FIGURE 1 intoproximity to the lower portion of the drum adjacent the permanent magnetassembly indicated generally by the reference numeral 13. The magneticsolids are attracted to the rotating drum surface by means of thepermanent magnet assembly 13 and carried through a series of magneticfields of successively 0pposite polarity associated with the permanentmagnet assembly to final magnetic discharge as indicated by the arrow 15in FIGURE 1. The non-magnetic solids with the bulk of the water arecarried to a tailing discharge as indicated diagrammatically by arrow 16in FIGURE 1. An operating water level may be maintained in theseparating zone as indicated diagrammatically by the dash line 18, forexample, with the excess water being carried oif through an overflowdischarge as indicated by the arrow 20.

As is well known in the art, suitable means may be provided forconfining the flow of the slurry feed introduced as indicated at 12 inFIGURE 1 to a region in close proximity to the drum periphery adjacentpoles 90, 91 and 92. The overflow indicated at 20 may be provided by avertical wall whose top horizontal edge is at the level indicated at 18in FIGURE 1 to prevent the liquid level from rising above this level.Suitable means is, of course, provided for collecting the concentratewhich is carried by the drum above the Water level for discharge bygravity or other suitable means generally as indicated by the arrow 15.

Referring to FIGURE 2, it will be observed that the drum 11 may comprisea cylindrical shell or material conveyor 30 having an exterior surfacefor receiving and conveying magnetic material to be separated. The shell3% is secured to annular rings 34 and 35 which in turn have end plates36 and 37 secured thereto by means of screws such as shown at 38. Theend plates 36 and 37 are journalled on stub shafts 4t} and 41 by meansof bearings such as indicated at 43 and 44-. The bearings are retainedon the shaft by means of caps 47 and 48 secured to the end plates 36 and37 by means of screws such as 50. Suitable seals are indicated at 53,54, and 56 for protecting the bearings. It will be understood that asprocket wheel is secured to one of the end plates 36 or 37 for rotatingthe drum 11 on stub shafts 40 and 41. Fixed supports for the stub shafts40 and 41 are indicated diagrammatically at 60 and 61.

The fixed permanent magnet assembly designated generally by thereference numeral 13 may comprise support plates and 71 of non-magneticmaterial secured by means of hubs 73 and 74 in fixed relation on thestub shafts 40 and 41. Suitable means may he provided externally of thedrum 11 for adjusting the angular position of the stub shafts '40 and 41to adjust the angular position of the magnet assembly. In operation ofthe separator, the stub shafts 40 and 41 are fixed. in a predeter minedangular position to maintain a predetermined fixed position of themagnet assembly such as indicated in FIGURE 1. Extending between thesupport plates 70 and 71 are a series of fiat holding plates ofnon-magnetic material 80, 81, 82 and 83. The lower margins 85 and 86 ofthe support plates 70 and 71 may be of arcuate configuration and definesegments of a circular are about the axis of shafts 4t) and 41 so as tobe concentric with the interior surface of the shell 30 and spaced fromthe interior surface substantially only the distance necessary toprovide a clearance gap accommodating rotation of the shell 30 relativeto the magnet assembly. It will be observed in FIGURE 1 that the holdingplates 80-83 define chords of the circular arc defined by the margin 85,so that the holding plates 80-83 are substantially as close as possibleto the interior surface of the shell 30.

Also extending between the support plates 70 and 71 and secured theretoare a series of magnetic pole pieces designated generally by thereference numerals 90, 91, 92, 93 and 94 formed of strips -118 ofmagnetic material. It will be observed from FIGURE 1 that the inner polepieces 91, 92 and 93 are of generally triangular configuration as seenin cross section. These pole pieces may be formed of a single solidwedge-shaped piece of magnetic steel if desired. By forming the polepieces of plates or strips such as 102, 103, 104, 105 and 106 for thepole piece 91 which are welded into the triangular configuration, areduction in the overall weight is achieved and the amount of machiningrequired to form the poles is reduced. Tests have shown that the weldedplate type pole piece as shown in FIGURE 1 has sufficient crosssectional area to carry the total flux introduced into these poles bythe permanent magnets. It will be observed that the lower margins of thepole pieces are substantially as close to the inner peripheral surfaceof the shell 30 as possible while still providing the necessaryclearance gap as with the holding plates 80-83.

As illustrated, the permanent magnet assemblies are provided by stacksof permanent magnet units such as indicated at 130 of standardizeddimensions. In the illustrated embodiment, the permanent magnets are arranged in two layers in the radial direction and two rows of stacks ineach layer as seen in FIGURE 2. Cover plates are indicated at 131, 132,133 and 134 in FIGURE 1 extending between the support plates 70 and 71and providing covers for the permanent magnets between the successivesets of pole pieces.

In the illustrated embodiment each of the permanent magnet units 130 ofa given stack'are magnetized in the same direction through the thicknessdimension of the permanent magnet slabs so as to provide directions ofmagnetization as indicated by arrows 150, 151, 152 and 153 in FIGURE 1.With these directions of magnetization, pole pieces 90, 92 and 94 may beconsidered of south magnetic polarity, While pole pieces 91 and 93 maybe considered of north magnetic polarity. In the illustrated embodiment,all of the permanent magnet units between a given set of pole pieces aremagnetized in the same direction to give a magnetic field of the samepolarity along the axial length of the drum at the exterior surface ofthe shell. Material carried along by the exterior surface of the shellduring rotation of the drum thus experiences successively a south poleat 90, a north pole at 91, a south pole at 92, a north pole at 93 and asouth pole at 94, after which the magnetic material is no longerattracted to the drum surface and is discharged as indi cated by thearrow in FIGURE 1.

It is found highly advantageous to utilize ceramic permanent magnetmaterial for the units 130 such as known by the trademark Indox V. Theutilization of permanent magnet materials for the energization source ofthe magnet assembly is, of course, a distinctive advantage as comparedto electromagnetic energization, since no external source of electricalenergy is required. The utilization of Indox V ceramic permanent magnetsprovides an improved energy source, enabling utilization of the totalmagnetic energy much more efiiciently than prior art structures. TheIndox V ceramic permanent magnet units can be suitably made into onespecific standard shape enabling the use of multiple numbers of this oneshape in various arrangements to eificiently construct magneticseparators of ditferent widths, of different diameter and of differentmagnetic intensities and field distributions.

A preferred system for varying the magnetic field strength is shown inFIGURES 1 and 2 as comprising a shorting armature or bar 170 mounted bymeans of a shaft 171 carried within the stub shafts 40 and 41 by meansof bearings 173, 174 and 175. The armature 170 is supported with theshaft 171 by means of support plates 176 and 177. Plates 176 and 177 aresecured to the shaft 171 by means of collars 180' and 181 receiving keys183 and 184 which extend into cooperating key ways in the collars and inthe shaft 171. Set screws are indicated at and 191 for retaining thekeys. An adjusting handle 195 may be provided at the outer end of shaft171 for adjusting the angular position of the armature 170 relative tothe permanent magnet assembly 13.

The armature 170 may comprise a plate of magnetic material such as mildsteel curved on a decreasing radius so as to provide shunt paths formagnetic flux from the respective permanent magnet stacks of differentreluctance. For example, in the position of the armature 170 shown inFIGURE 1, a portion of the armature is relatively closely spaced to polepiece plates 106 and 107 to provide a relatively large shunting effectbetween poles 91 and 92, thereby decreasing the useful magnetic fieldstrength between these poles at the exterior of the drum. The reluctanceof the shunt path is substantially greater between poles 93 and 94 toprovide a maximum field strength between poles 93- and 94 at theexterior surface of the drum 11.

Since the armature is curved on a decreasing radius, it is possible tovary the distance between the armature and the radially innerextremities of strips 101, 102-, 106, 107, 111, 112, 116 and 117 byrotation of the armature. FIGURE 1 shows the armature in three of itspossible positions. In the position shown in solid lines in FIG- URE 1,the armature is in close proximity to the poles shorting out the maximumamount of magnetic flux, and thereby providing the minimum magneticfield strength at the exterior surface of the drum. In the positionindicated in dot-dash outline at 170a, the armature is positionedsubstantially out of the influence of the magnetic poles, therebyproviding the maximum field intensity at the surface of the drum. Theposition indicated at 17012 is an intermediate position, shorting outonly a small amount of the magnetic flux of the first three poles 90, 91and 92, and giving only a slight reduction of the magnetic intensity atthese poles with respect to the exterior surface of the drum. Thearmature may, of course, be positioned in any orientation between thesolid line position and the positions indicated at 17% and 17011 to varythe working magnetic field strength anywhere between full strengthcorresponding to the position indicated at 170:: to a 60% reduction ofworking magnetic field strength in the position shown in solid lines inFIG- URE 1.

In operation of the embodiment of FIGURES 1 and 2, the cylinder 30 isrotated in the clockwise direction as indicated by arrow 197 andmaterial is fed beneath the first pole 90. Magnetic material is liftedto the rotating cylinder 30 and transported from pole to pole forultimate discharge upon leaving the influence of the last magnetic pole94. Experience has shown that the greatest control of quality ofmagnetic separation occurs in the initial magnetic pick-up zone orthrough the area of the first three magnetic poles 90, 91 and 92. This,therefore, is the zone in which the maximum control of magnetic fieldstrength is desired. The last two poles 93 and 94 are used fortransportation of the magnetic material to eventual discharge, so thatit is desired to have less reduction of field strength at these last twodischarge poles. The configuration of the shorting armature as shown inFIGURE 1 provides the maximum variable control in the initial pick-upzone at poles 90-92. The leakage flux paths between the successive polesare indicated by arrows 200, 201, 202 and 203, and it will be observedthat the reluctance of the shunt flux paths may be substantiallycontinuously varied over a relatively wide range by adjusting theangular position of the armature 170.

FIGURE 3 illustrates a modified armature 210 of magnetic material formedon substantially a constant radius, but with portion 210a thereof havinga substantially greater thickness than portion 210!) and portion 21%having substantially twice the thickness of portion 2100 to provide avariable reluctance in the shunt'magnetic paths i dicated by arrows200-203 in FIGURE 1. FIG- URE 3 is otherwise identical to FIGURE 1, andcorresponding reference numerals have been applied to similar parts.

In FIGURE 4, a shorting armature 220 of magnetic material is illustratedwhich may be formed on a constant radius, but wherein the reluctance ofthe shunt paths is made variable by virtue of the serrated shape of thearmature which provides a progressively decreasing cross sectional areaat the regions 220a of the armature. It is also possible to accomplish avariation in the magnetic field strength by mounting the armature ofFIGURES 1, 3 or 4 for movement toward or away from the permanent magnetassembly. In this case, the armature would not need to rotate about anaxis, but would be mounted in such a manner as to be translated as aunit in a direction along a diameter of the drum, for example.

FIGURE 5 illustrates a second embodiment of the present invention whichis generally similar to the embodiment of FIGURES 1 and 2, but involvesa dry process for concentrating magnetic materials. In this embodiment,a drum 250 may have the same general construction and mounting asillustrated in FIGURE 2 and may rotate in the direction indicated byarrow 251. Material to be separated in a dry form is delivered bysuitable means such as diagrammatically indicated at 253 onto the drumat the top thereof in the direction indicated by arrow 255. Theseparator may be provided with adjustable division vanes for separatingthe material falling from the surface of the drum into three dischargestreams as indicated by arrows 260, 261 and 262 in FIG- URE 5.

The permanent magnet assembly designated generally by the referencenumeral 270 may be of the same construction described in detail inreference to FIGURE 1 to provide a succession of poles of alternatingpolarity designated by the reference numerals 280-288. The permanentmagnet assembly is essentially the same as that illustrated in FIGURE 1,except that additional stacks of permanent magnet units 130 andadditional triangular pole pieces are provided to increase theperipheral extent of the permanent magnet assembly. As described inconnection with FIGURE 1, the magnetic poles are each of the samepolarity and of uniform strength across the entire axial extent of thedrum. In operation, the feed falls on the revolving drum at the firstmagnetic pole 280 and as it does it receives a definite magneticpolarity. The second magnet pole 281 has a reverse polarity from thefirst, and as the material passes the second pole, the magneticallyresponsive fraction of the feed tends to shift and reorient itself. Thisagitation and reorientation releases some of the entrapped non-magneticmaterial and permits it to fall free as indicated by arrow 260. Theprocess is then repeated for the third and succeeding magnet poles, andeach provides a further magnetic material movement and cleaning. Theresults is an exceptionally clean magnetic product coming from theconcentrate zone as indicated by the arrow 262. The material which doesnot discharge as tailings as indicated by arrow 260 and yet is notsufficiently magnetic to concentrate may be independently obtained in amiddling zone indicated by arrow 261.

As in the embodiment of FIGURES 1 and 2, the permanent magnet assemblypreferably comprises stacks of permanent magnet units or slabs.130 ofIndox V ceramic material arranged in layers and rows between triangularpole pieces, with the stacks between each set of pole pieces magnetizedthrough their thickness direction as indicated by arrows 290-297 inFIGURE 5.

The leakage flux paths between the successive poles are indicated byarrows 300-307, and as in the embodiment of FIGURE 1, an armature 320 ofmagnetic material is mounted on a central shaft 321 so as to beangularly adjustable to vary the reluctance of the shunt magnetic fluxpaths and thereby vary the strength of the working 6 fields between thesuccessive poles at the periphery of the drum.

In the dry magnetic separator of the type shown in FIGURE 5, maximumremoval of non-magnetic material and purification of the magneticmaterial. occurs as the magnetic material is transported by the rotatingcylinder beyond the horizontal center line, so that non-magneticmaterial may drop away by gravity. Therefore, with this type of magneticseparator, the greatest control of magnetic strength is desired in thelower or discharge zone of the magnetic assembly represented by poles284288. The orientation of the decreasing radius of the shortingarmature 320 is therefore opposite to that shown in FIGURE 1 with theradius increasing in the direction of drum rotation in FIGURE 5 ratherthan decreasing in the direction of drum rotation as in FIGURE 1. Thisenables a variation of magnetic field strength from the position ofminimum magnetic field of the armature shown in solid lines in FIGURE 5through an intermediate position shown at 320a to a position of maximumworking field strength indicated at 32%.

In the commercial application of this invention, some designs have theIndox V magnets operating at a permeance coefficient near the knee ofthe demagnetization curve. If the magnets are then subjected to lowtemperatures in shipment or at the operating site, it is possible thatthe magnets will have a permanent flux drop unless suitable precautionsare provided to guard against this flux drop.

The use of the adjustable armature is an excellent precaution againstthis fiux drop. With the armature in position to provide an auxiliarypath for the magnetic flux, the permeance coefficient of the magnets israised sufliciently above the knee of the demagnetization curve,enabling the magnets to be subjected to temperatures as low as minus 40F. without experiencing any drop in magnetic flux.

It will be apparent that many modifications and variations may beeffected without departing from the scope of the novel concepts of thepresent invention.

I claim as my invention:

1. In a magnetic separator comprising a conveyor having a surface forreceiving material to be separated and a magnet assembly for tending toattract magnetic material toward the conveyor surface for movementtherewith to separate the same from non-rnagnetic material, theimprovement characterized by means defining a shunt magnetic flux pathfor magnetic flux from said magnet assembly, and means for adjusting thereluctance of said shunt magnetic flux path without substantiallychanging the reluctance of the working magnetic flux path of the magnetassembly to adjust the strength of the magnetic field provided by saidmagnet assembly at the surface of said conveyor.

2. In a magnetic separator comprising a conveyor having a surface forreceiving material to be separated and a magnet assembly for tending toattract magnetic material toward the conveyor surface for movementtherewith, the improvement characterized by means defining a magneticflux path of magnetic material at the side of the magnet assembly remotefrom the conveyor for shunting a predetermined proportion of themagnetic =fiux of said magnet assembly away from the working flux pathat said conveyor surface and for selective positioning at a plurality ofpositions relative to said magnet assembly.

3. In combination with a magnetic separator drum mounted for rotation ona longitudinal axis and a permanent magnet assembly mounted at a fixedangular position within said drum, an armature of magnetic materialdisposed in said drum in proximity to said permanent magnet assembly,and means for selectively positioning said armature at a plurality ofpositions for adjusting the reluctance of the magnetic leakage pathincluding said armature for magnetic flux from said permanent magnetassembly while the reluctance of the working magnetic flux path of thepermanent magnet assembly remains sub- 'stantially the same.

4. In combination with a conveyor for receiving material to be separatedand a magnet assembly for tending to attract magnetic material towardthe conveyor for movement therewith, the improvement characterized by anarmature of magnetic material disposed adjacent said permanent magnetassembly within the influence of the magnetic field thereof, and meansfor adjustably mounting said armature to adjust the strength of theuseful magnetic field of said magnet assembly.

5. In a magnetic separator comprising a conveyor for receiving andtransporting material to be separated and a magnet assembly for tendingtoattract magnetic material toward the conveyor for movement therewith,said mag net assembly comprising spaced pole pieces extending generallytransversely to the conveyor from a point adjacent the inner surface ofthe conveyor to a point more remote from the conveyor, a series ofpermanent magnet slabs stacked between the successive pole pieces andmagnetized generally in the direction of movement of the conveyor, andmeans of magnetic material disposed within the magnetic field betweenthe successive pole pieces at the sides thereof remote from saidconveyor for diverting magnetic flux from the working flux path of themagnet assembly and for selective positioning at a plurality ofpositions relative to said poles to selectively adjust the leakagereluctance therebetween.

6. In a magnetic separator comprising a conveyor for receiving andtransporting material to be separated and a magnet assembly for tendingto attract magnetic material toward the conveyor for movement therewith,said magnet assembly comprising spaced pole pieces extending generallytransversely to the conveyor from a point adjacent the inner surface ofthe conveyor to a point more remote from the conveyor, a series ofpermanent magnet slabs stacked between the successive pole pieces andmagnetized generally in the direction of movement of the conveyor, andmeans of magnetic material disposed within the magnetic field betweenthe successive pole pieces at the sides thereof remote from saidconveyor for diverting magnetic flux from the working flux path of themagnet assembly, and means for adjustably mounting said means ofmagnetic material to adjust the strength of the useful magnetic fieldfrom said permanent magnet assembly.

7. In combination, a magnetic separator drum of nonmagnetic material, apair of stub shafts mounting said drum for rotation on a longitudinalaxis, a permanent magnet assembly mounted within said drum from saidstub shafts for angular adjustment by means of rotation of said stubshafts, an armature of magnetic material mounted at the inner side ofsaid permanent magnet assembly for adjusting the useful magnetic fieldstrength thereof, and a shaft extending within one of said stub shaftsand mounting said armature for adjustment relative to said permanentmagnet assembly to adjust the useful magnetic field strength thereof.

8. In combination, a magnetic separator drum of nonmagnetic material, apair of stub shafts mounting said drum for rotation on a longitudinalaxis, a permanent magnet assembly mounted within said drum from saidstub shafts, for angular adjustment by means of rotation of said stubshafts, an armature of magnetic material mounted at the inner side ofsaid permanent magnet assembly for adjusting the useful magnetic fieldstrength thereof, and a shaft extending within one of said stub shaftsand mounting said armature for adjustment relative to said permanentmagnet assembly to adjust the useful magnetic field strength thereof,said armature comprising a strip of magnetic material of curvedconfiguration and of decreasing radius.

9. In combination, a magnetic separator drum of nonmagnetic material, apair of stub shafts mounting said drum for rotation on a longitudinalaxis, a permanent magnet assembly mounted within said drum from saidstub shafts for angular adjustment by means of rotation of said stubshafts, an armature of magnetic material mounted at the inner side ofsaid permanent magnet assembly for adjusting the useful magnetic fieldstrength thereof, and a shaft extending within one of said stub shaftsand mounting said armature for adjustment relative to said permanentmagnet assembly to adjust the useful magnetic field strength thereof,said armature comprising a curved piece of magnetic material ofprogressively varying thickness.

10. In combination, a magnetic separator drum of nonmagnetic material, apair of stub shafts mounting said drum for rotation on a longitudinalaxis, a permanent magnet assembly mounted within said drum from saidstub shafts for angular adjustment by means of rotation of said stubshafts, an armature of magnetic material mounted at the inner side ofsaid permanent magnet assembly for adjusting the useful magnetic fieldstrength thereof, and a shaft extending within one of said stubshafts'and mounting said armature for adjustment relative to saidpermanent magnet assembly to adjust the useful magnetic field strengththereof, said armature comprising a curved plate of magnetic materialhaving V- shaped notches therein to provide a progressively decreasinglongitudinal cross section at one end thereof.

References Cited in the file of this patent UNITED STATES PATENTS1,324,529 Ulh'ich Dec. 9, 1919 2,785,801 Laurila Mar. 9, 1957 FOREIGNPATENTS 461,816 Great Britain Feb. 25, 1937

